Note: Descriptions are shown in the official language in which they were submitted.
~74891
TITLE
PROCESS ~OR SURFACE TREAT~NT OF
FLEXOGRAPHIC PRINTING PLATES CONTAINI~G
BUTADIENE/ACRYLONITRILE COPOLYM~RS
5DESCRIPTION
TECHNICAL FIELD
This invention relates to ~ process for
surface treatment of photosensitive flexographic
printing plates. More particularly this invention
relates to the surface treat~.ent of flexographic
printing plates wherein the photosensitive layer
contains a butadiene/acrylonitrile copolymer. Still
more particularly this invention relates to the
surface treatment of a photosensitive layer
containing butadiene/acrylonitrile copolymer with
bromine.
BACKGROUND ART
Photosensitive flexographic printing plates
are becoming more important in the printing trade.
Particularly useful compositions for preparing such
flexographic printing plates include: compositions
containing addition-polymerizable, ethylenically
unsaturated compounds, photoinitiators and as
polymeric binders either block copolymers such as
styrene-butadiene-styrene and
styrene-isoprene-styrene polymers, or
butadiene/acrylonitrile polymers with optional
carboxyl groups. The printing plates utilizing
compositions containing said block copolymers are
generally compatible only with alcohol or
alcohol-acetate based inks; while printing plates
utilizing compositions containing
butadiene/acrylonitrile polymers with optional
c~rboxyl groups are general1y only compatible with
-~D-1889 35 hydrocarbon based inks.
~:174~
The flexographic printing plates containing
styrene-butadiene-styrene or styrene-isoprene-styrene
block copolymer binders, after imagewise exposure and
development, are generally treated with an acid
hypochlorite solution to reduce the tackiness of the
layer. A reduction in tackiness can also be achieved
by use of a bromine solution; however, neither
chlorine nor bromine treatment renders printing
plates based on these block copolymers compatible
with hydrocarbon based inks.
Flexographic printing plates containing a
butadiene/acrylonitrile polymer with o~tional
carboxyl groups, however, are not only tacky but are
susceptible to attack by certain solvents and other
components present in some printing inks, e.g.,
alcohols, acetates, etc. Use of these plates is
limited therefore to a restricted class of inks
containing substantially hydrocarbon solvents. The
use of a chlorine-containing solution such as a
hypochlorite solution may alleviate the tackiness
problem but does not prevent the printing surface of
the printing plate from being attacked by inks
containing alcohols and various other solvents.
Surprisingly, the butadiene/acrylonitrile
polymer-containing flexographic printing plates, when
treated with an aqueous solution having a free
bromine concentration, either before or after
postexposure, exhibit an increase in solvent
resistance to all inks, and most notably in
resistance to alcohol containing inks and various
`~ other nonhydrocarbon solvents. This is not observed
with chlorine treatment, and it is also not observed
with either chlorine or bromine treatment of
styrene-isoprene-styrene or styrene-butadiene-styrene
block copolymer-containing printing plates.
117489~.
An object of the invention is to provide a
bromination process which renders printing plates
prepared from photosensitive compositions containing
butadiene/acrylonitrile polymers with optional
carboxyl groups compatible with alcohol-based inks as
well as hydrocarbon based inks. Another object of
the invention is to provide a process wherein the
bromination treatment can occur prior to or
subse~uent to postexposure. ~till another object of
the invention is to provide a process for immediate
b;omine treatment of said printing plates which have
been aqueous developed without the necessity of
drying.
DISCLOSURE OF THE INVENT~ON
In accordance with this invention there is
provided a process for providing improved solvent
resistant surfaces of relief flexographic printing
plates wherein the reliefs are prepared by imagewise
exposure with actinic radiation and liquid
d~velopment of the unexposed areas of a layer of a
photosensitive, elastomeric composition comprising a
high molecular weight butadiene/acrylonitrile
copolymer having a number average molecular weight of
20,000 to 75,000, an acrylonitrile content of 10 to
25 50% by weight and a carboxyl content of 0 to 15% by
weight and a nongaseous ethylenically unsaturated
compound containing at least one terminal ethylenic
- gro~p, the improvement, wherein after drying, the
developed surface is, in either order,
(1) postexposed to a source of actinic
radiation, and
(2) contacted with an a~ueous solution
having a free bromine concentration of 0.01 to 3.5
by weight for about 15 seconds to 20 minutes.
.~
117~gl
The photosensitive compositions used in the
process of this invention comprise a high molecular
weight butadiene/acrylonitrile copolymer, a
nongaseous, ethylenically unsaturated compound, an
organic, radiation-sensitive, free-radical generating
photoinitiator or system as well as other additives
discussed below. The compositions may be used in
layer form or the layer may be adhered to flexible
supports or a temporary support may be used. Useful
flexible supports include: plastic films and metal
sheets, open or closed cell foams, compressible
rubber layers, or a combination of foams and rubber
layers with plastic films. When the combination
support is used the plastic film is generally
adjacent to the photosensitive layer. Examples of
such supports include: polymeric film supports
such as polyethylene terephthalate, flame-treated
polyethylene terephthalate, electron-discharge
treated polyethylene terephthalate, polyimide, e.g.,
film as disclosed in U.S. Patent 3,179,634, etc.,
and thin metal supports such as aluminum, tin-plated
steel (dull or shiny). The polymeric supports
generally have a thickness in the range of 0.001
inch to 0.007 inch (0.025 to 0.18 mm). The metal
supports generally have a thickness in the range of
0.010 to 0.0115 inch (0.25 to 0.29 mm) for aluminum
and 0.008 to O.nlO inch (0.20 to 0.25 mm) for
tin-plated steel. Examples of foam supports include
open or closed cell foams, e.g., polyvinyl chloride,
polyurethane, ethylenepolylenediene rubher, neoprene,
etc. Examples of compressible rubbers include:
styrene/isoprene block copolymers,
butadiene/acrylonitrile copolymers, natural rubber,
etc.
1~74~391
The photosensitive compositions disclosed
herein are developable in their unexposed state in
aqueous, semiaqueous basic, or solvent solutions
depending on the carboxyl content of the polymeric
binder component of the photosensitive composition.
The photosensitive layers are in the thickness range
of 0.0005 to 0.250 inch (about 0.013 to 6.35 mm) or
more.
One essential ingredient of the
photosensitive, elastomeric composition is a high
molecular weight butadiene/acrylonitrile copolymer
(a) having a number average molecular weight (Mn) in
the range of about 20,000 to about 75,000, preferably
in the range of about 25,000 to about 50,000. The Mn
lS for the polymers described herein can be determined
by gel permeation chromatography employing a
butadiene standard. The acrylonitrile content of the
polymers varies from about 10 to about 50% by weight,
preferably from about 15 to about 40%. Optionally,
the copolymer also has a carboxyl content of 0 to
about lS~ by.weight. When the copolymer contains
carboxyl groups, the carboxyl content is preferably
in the range of about 1 to about 15%, most preferably
in the range of about 2 to about 10% by weight. The
copolymer is present in an amount of about 55 to 90%
by weight, based on the total weight of the
composition, and preferably about 60 to about 75% by
weight. At least about 55% by weight of the
copolymer is necessary to give adequate flexibility
and physical integrity to the photosensitive
elements, particularly for flexographic plates.
Carboxyl groups may be incorporated into the
high molecular weight copolymer by addition to the
polymerization process of a carboxyl containing5 monomer, e.g., acrylic or methacrylic acid, or a
~174~91
monomer which is converti~le to a carboxyl containing
group, e.g., maleic anhydride or methyl
methacrylate. Such polymers are available
commercially from several sources, e.g., from the
B. F. Goodrich Chemical Company under the trade name
Hyca~D.
Another essential ingredient of the
photosensitive compositions of this invention is a
nongaseous, ethylenically unsaturated compound
containing at least one terminal ethylenic group
(b). This compound should be capable of forming a
high polymer by free-radical initiated
chain-propagating addition polymerization and be
compatible with the high molecular weight polymers
(a) described above. One class of suitable
ethylenically unsaturated compounds includes
unsaturated esters of alcohols, especially such
esters of alpha-methylene carboxylic acids and
substituted alpha-methylene carboxylic acids, more
especially such esters oE alkylene polyols and
polyalkylene polyols, and most especially alkylene
polyol di- and tri-acrylates and polyalkylene polyol
di- and tri-acrylates prepared from alkylene polyols
of 2-15 carbon atoms or polyalkylene ether polyols or
glycols of 1-10 ether linkages.
The following specific compounds are further
illustrative of this class: ethylene glycol
diacrylate, diethylene glycol diacrylate, glycerol
diacrylate, glycerol triacrylate, trimethylolpropane
triacrylate, ethylene glycol dimethacrylate,
1,3-propanediol dimethacrylate, 1,2,4-butanetriol
trimethacrylate, 1,4-cyclohexanediol diacrylate,
1,4-benzenediol dimethacrylate, 1,2-benzenedimethanol
diacrylate, pentaerythritol triacrylate,
35 pentaerythritol tetramethacrylate, 1,3-propanediol
~74t~1
diacrylate, 1,3-pentanediol dimethacrylate, p-alpha,
alpha-dimethylbenzylphenyl acrylate, t-butyl
acrylate, N,N-diethylaminoethyl acrylate,
diethylaminoethyl methacrylate, l,4-butanediol
diacrylate, hexamethylene glycol diacrylate,
decamethylene glycol diacrylate, 2,2-dimethylolpropane
diacrylate, tripropylene glycol diacrylate, 2,2-
di(p-hydroxyphenyl)propane diacrylate, 2,2-di(p-
hydroxyphenyl)propane dimethacrylate, polyoxyethyl-
2,2-di(p-hydroxyphenyl)propane triacrylate (molecular
weight of 462), 1,4-butanediol dimethacrylate,
hexamethylene glycol dimethacrylate, 2,2,4-trimethyl-
1,3-pentanediol dimethacrylate, 1-phenylethylene-1,2-
dimethacrylate, trimethylolpropane trimethacrylate,
triethylene glycol diacrylate, ethylene glycol
acrylate phthalate, polyoxyethyltrimethylolpropane
triacrylate, diacrylate and dimethacrylate esters of
diepoxy polyethers derived from aromatic polyhydroxy
compounds such as bisphenols, novolaks and similar
compounds such as those described by ~rary in U.S.
Patent 3,661,576, the bis-acrylates and methacrylates
of polyethylene glycols of molecular weight 200-500,
etc.
Another class of suitable ethylenically
unsaturated compounds includes the compounds disclosed
by Martin and Barney in U.S. Patent 2,927,022, e.g.,
those having a plurality of addition polymerizable
ethylenic linkages, particularly when present as
terminal linkages, and especially those wherein at
least one and preferably most of such linkages are
conjugated with a double bonded carbon, including
carbon double bonded to carbon and to heteroatoms
lX7489~
such as nitrogen, oxygen and sulfur. Preferred are
such materials wherein the ethylenically unsaturated
groups, especially the vinylidene groups, are
conjugated with ester or amide structures. Specif~c
examples of such compounds include unsaturated
amides, particularly those of alpha-methylene
carboxylic acids, especially with
alpha-omega-diamines and oxygen-interrupted
omega-diamines, such as methylene bis-acrylamide,
methylene bis-methacrylamide, ethylene
bis-methacrylamide, 1,6-hexamethylene bis-acrylamide,
diethylene triamine trismethacrylamide,
bis( methacrylamidopropoxy)ethane,
betamethacrylamidoethyl methacrylate,
N-(beta-hydroxyethyl)-beta-(methacrylamido)ethyl
acrylate, and N,N-bis(beta-methacryloxyethyl)
acrylamide; vinyl esters such as divinyl succinate,
divinyl adipate, divinyl phthalate, divinyl
terephthalate, divinyl benzene-1,3-disulfonate, and
divinyl butane-1,4-disulfonate; diallyl fumarate; etc.
Additional ethylenically unsaturated
compounds which may be used include styrene and
derivatives thereof: 1,4-diisopropenylbenzene,
1,3,5-triisopropenyl-benzene; itaconic anhydride
adducts with hydroxyethyl acrylate (1:1), itaconic
anhydride adducts with liquid butadiene/acrylonitrile
polymers containing terminal amino groups, and
itaconic anhydride adducts with the diacrylate and
dimethacrylate esters of diepoxy polyethers described
in Crary U.S. Patent 3,661,576; polybutadiene and
butadiene/acrylonitrile copolymers containing
terminal and pendant vinyl groups; and unsaturated
aldehydes, such as sorbaldehyde (2,4-hexadienal).
Ethylenically unsaturated compounds which5 are water soluble or contain carboxyl or other
i~74~391
alkali-reactive groups are especially suitable when
aqueous basic-developable systems are involved.
In addition, the polymerizable, ethylenically
unsaturated polymers of Burg, U.S. Patent 3,043,805;
Martin, U.S. Patent 2,929,710; and similar materials
may be used alone or mixed with other materials.
Acrylic and methacrylic esters of adducts of ethylene
oxide and polyhydroxy compounds such as those
described by Cohen and Schoenthaler in U.S. Patent
3,380,831 are also useful. The photocrosslinkable
polymers disclosed in Schoenthaler, U.S. Patent
3,418,295, and Celeste, U.S. Patent 3,448,089, may
also be used.
The amount of unsaturated compound added
should be in the range of about 2 to about 40% by
weight, based on the total weight of composition.
The specific amount for optimum results will vary
depending on the particular polymers used.
Preferably the amount of unsaturated compound is
in the range of about 5 to about 25%.
The ethylenically unsaturated compound
preferably has a boiling point at normal pressure of
over about 100C. The most preferred ethylenically
unsaturated compounds are triethylene glycol
diacrylate, triethylene glycol dimethacrylate,
hexamethylene glycol dimethacrylate and
hexamethylene glycol diacrylate.
The photosensitive compositions of this
invention substantially do not scatter actinic
radiation when in the form of thin layers, as
described above. In order to secure a substantially
transparent mixture, i.e., a nonradiation-scattering
mixture, the butadiene copolymer and polymer
components should be compatible with, and preferably
rs~
1174?391
soluble in, the ethylenically unsaturated compound in
the proportions used.
By "compatible" is meant the ability of two
or more constituents to remain dispersed in one
another without causing any significant amount of
scattering of actinic radiation. Compatibility is
often limited by the relative proportions of the
constituents, and incompatibility is evidenced by
formation of haze in the photosensitive composition.
Some slight haze can be tolerated from such
compositions before or during exposure in the
preparation of printing reliefs, but when fine detail
is desired, haze should be completely avoided. The
amount of ethylenically unsaturated compound, or any
other constituent, used is therefore limited to those
concentrations which do not produce undesired light
scatter or haze.
Another essential ingredient of the
photosensitive compositions of this invention is an
organic, radiation-sensitive, free-radical generating
system (c). Practically any organic,
radiation-sensitive, free-radical senerating system
which initiates polymerization of the unsaturated
compound and does not excessively terminate the
polymerization can be used in the photosensitive
compositions of this invention. The term "organic"
is used here and in the claims to designate compounds
which contain carbon, and one or more of oxygen,
hydrogen, nitrogen, sulfur and halogen, but no
30 metal. Because process transparencies transmit heat
originating from conventional sources of actinic
radiation, and since the photosensitive compositions
are usually prepared under conditions resulting in
elevated temperatures, the preferred free-radical5 generating compounds are inactive thermally below
1174f~
11
85C and more preferably below 185C. They should be
dispersible in the composition to the extent
necessary for initiating the desired polymerization
or crosslinking under the influence of the amount of
radiation absorbed in relatively short term
exposures. These initiators are useful in amounts
from about 0.001 to about 10% by weight, and
preferably from about 0.1 to about 5~ based on the
total weight of the solvent-free photosensitive
composition.
The free-radical generating system absorbs
radiation within the range of about 2000 to about
8000 A and has at least one component that has an
active radiation absorption band with molar
lS extinction coefficient of at least about 50 within
the range of about 2500 to about 8000 A, and
preferably about 2500 to about 5000 A. The term
"active radiation absorption band" means a band of
radiation which is active to produce the free
radicals necessary to initlate polymerization or
crosslinking of the unsaturated material.
The free-radical generating system can
comprise one or more compounds which directly furnish
free radicals when activated by radiation. It can
also comprise a plurality of compounds, one of which
yields the free radicals after having been ca~sed to
do so by a sensitizer which is activated by the
radiation.
A large number of such free-radical
generating compounds can be utilized in the practice
of the invention and include aromatic ketones such as
benzophenone, Michler's '~etone
[4,4'-bis(dimethylamino)benzophenone],
4,4'-bis(diethylamino)benzophenone,5 4-acryloxy-4i-dimethylaminobenzophenone,
11
~4~
12
4-acryloxy-4'-diethylaminobenzophenone, 4-methoxy-
4'-dimethylaminobenzophenone, 2-phenyl-2,2-
dimethoxyacetophenone (2,2-dimethoxy-1,2-dipheny~
ethanone), 2-ethylanthraquinone, phenanthraquinone,
2-t-butylanthraquinone, 1,2-benzanthraquinone,
2,3-benzathraquinone, 2,3-dichloronaphthoquinone,
benzil dimethyl acetal, and other aromatic ketones;
benzoin, benzoin ethers such as benzoin methyl ether,
benzoin ethyl ether, benzoin isobutyl ether, and
benzoin phenyl ether, methylbenzoin, ethylbenzoin and
other benzoins; and 2,4,5-triarylimidazolyl dimers
such as 2-(o-chlorophenyl)-4,5-diphenylimidazolyl
dimer, 2-(o-chlorophenyl)-4,5-di(m-methoxyphenyl)-
imidazolyl dimer, 2-(o-fluorophenyl)-4,5-
diphenylimidazolyl dimer, 2-(o-methoxyphenyl)-4,5-
diphenylimidazolyl dimer, 2-(p-methoxyphenyl)-4,5-
diphenylimidazolyl dimer, 2,4-di(p-methoxyphenyl)-5-
phenylimidazolyl dimer, 2-(2,4-dimethoxyphenyl)-4,5-
diphenylimidazolyl dimer, 2-(p-methylmercaptophenyl)-
4,5-diphenylimidazolyl dimer, etc., as disclosed in
U.S. Patents 3,479,185 and 3,784,557 and in British
Patents 997,396 and 1,047,569.
The imidazolyl dimers can be used with
a free-radical producing electron donor such as
2-mercaptobenzoxazole, Leuco Crystal Violet or
tri(4-diethylamino-2-methylphenyl)methane. Such
sensitizers as Michler's ketone may be added.
Various energy transfer dyes such as Rose Bengal
and Eosin Y can also be used. Additional examples
of suitable initiators are disclosed by Plambeck
in U.S. Patent 2,760,863.
The photosensitive compositions may
also contain a small amount of thermal addition
12
~1~4891
13
polymerization inhibitor, e.g., 0.001% to 2.0%,
based on the weight of the total solvent-free
photosensitive composition. Suitable inhibitors
include hydroquinone and alkyl and aryl-substituted
hydroquinones, 2,6-di-tert-butyl-4-methylphenol,
p-methoxyphenol, tert-butylpyrocatechol, pyrogallol,
beta-naphthol, 2,6-di-tert-butyl-p-cresol,
phenothiazine, pyridine, nitrobenzene, dinitrobenzene
and the nitroso dimer inhibitor systems described
in U.S. Patent 4,168,982. Other useful inhibitors
include p-toluquinone, chloranil and thiazine dyes,
e.g., Thionine Blue G (CI 52025), Methylene Blue B
(CI 52015) and Toluidine Blue (CI 52040). Such com-
positions can be photopolymerized or photocrosslinked
without removal of the inhibitor. The preferred
inhibitors are 2,6-di-tert-butyl-4-methylphenol and
p-methoxyphenol.
The oxygen and ozone resistance of
photosensitive elements of this invention and
printing reliefs made therefrom can be improved by
incorporating into the photosensitive composition a
suitable amount of compatible well known antioxidants
and/or antiozonants. Antioxidants useful in this
invention include: alkylated phenols, e.g., 2-6-di-
tert-butyl-4-methylphenol; alkylated bis-phenols,
e.g., 2,2-methylene-bis-(4~methyl-6-tert-butylphenol);
1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-
hydroxybenzyl)benzene; 2-(4-hydroxy-3,5-di-tert-
butylanilino)-4,6-bis-(n-octyl thio)-1,3,5-triazine;
polymerized trimethyldihydroquinone; and dilauryl
thiopropionate.
Antiozonants useful in this invention
include: microcrystalline wax and paraffin wax;
dibutylthiourea; 1,1,3,3-tetramethyl 2-thiourea;
13
~74~391
-- 14
Antiozonant AFD, a product of Nafton Co.;
norbornenes, e.g., di~5-norbornene-2-methyl adipate,
di-5-norbornene-2-methyl terephthalate; Ozone
Protector* 80, a product of Reichhold Chemical Co.;
N-phenyl-2-naphthylamine; unsaturated vegetable oils,
e.g., rapeseed oil, linseed oil, safflower oil;
polymers and resins, e.g., ethylene/vinyl acetate
copolymer resin, chlorinated polyethylene,
chlorosulfonated polyethylene, chlorinated
ethylene/methacrylic acid copolymer, polyurethanes,
polypentadienes, polybutadiene, furfural-derived
resins, ethylene/propylene/diene rubber, diethylene
glycol ester of rosin and alpha-methylstyrene/
vinyltoluene copolymer. Ozone resistance of the
printing relief produced can also be improved by
annealing it at elevated temperatures prior to use.
If desired, the photosensitive compositions
can also contain immiscible, polymeric or nonpoly-
meric organic or inorganic fillers or reinforcing
agents which are essentially transparent at the
wavelengths used for exposure of the photosensitive
material and which do not scatter actinic radiation,
e.g., polystyrene, the organophilic silicas,
bentonites, silica, powdered glass, colloidal carbon,
as well as various types of dyes and pigments. Such
materials are used in amounts varying with the
desired properties of the elastomeric compositions.
The fillers are useful in improving the strength of
the elastomeric layer, reducing tack and, in addition,
as coloring agents.
The photosensitive layer preferably
contains a compatible plasticizer to lower the glass
transition temperature of the binder and facilitate
selective development. The plasticizer may be any of
the common plasticizers compatible with the polymeric
* denotes trade mark
14
~174891
binders. Among the common plasticizers are dialkyl
phthalates, alkyl phosphates, polyethylene glycol,
polyethylene glycol esters, and polyethylene glycol
ethers. Other useful plasticizers include oleic
acid, lauric acid, etc. Polyesters are preferred
plasticizers, e.g., polyethylene sebacate, etc. The
plasticizer is generally present in an amount of l to
15% by weight based on weight of total solids of the
photosensitive composition.
The photosensitive compositions of this
invention can be prepared in any suitable way by
mixing the ingredients, i.e., (a) the high molecular
weight butadiene/acrylonitrile copolymer, (b) the
compatible ethylenically unsaturated compound, and
(c) the free-radical generating system. ~or example,
flowable compositions can be made by mixing them and
other desired adjuvants in any order and, if desired,
with the aid of a solvent such as chlorinated
hydrocarbons, e.g., methylene chloride, chloroform,
methyl chloroform, chlorobenzene, trichloroethylene,
tetrachloroethylene and chlorotoluene; ketones, e.g.,
methyl ethyl ketone, diethyl ketone and methyl
isobutyl ketone; aromatic hydrocarbons, e..g.,
benzene, toluene and xylene; and tetrahydrofuran.
The above solvents can contain as diluents acetone;
lower molecular weight alcohols, e.g., methyl, ethyl
and propyl alcohol; and esters, e.g., methyl, ethyl
and butyl acetate. The solvent can be removed later
by heating the admixture or extruded layer.
Conventional milling, mixing, and solution
techniques can be used in making these compositions,
the particular technique varying with the differences
in properties of the respective components. The
homogeneous, substantially nonradiation-scattering5 compositions, are formed into sheets in any desired
11'7~891
16
manner. For example, solvent-casting, hot pressing,
calenderins, or extrusion are suitable methods for
preparing layers of the desired thickness.
The photosensitive elements of this
invention can be made by solvent casting or by
extruding, calendering or pressing at an elevated
temperature of the photosensitive composition into
the form of a layer or self-supporting sheet on a
suitable casting wheel, belt or platen. The layer or
sheet may be laminated to the surface of the flexible
support described above and may be adhered by means
of an adhesive blend as described below. When a
solution is used the coating may be made on an
adhesive-bearing support.
The thickness of the photosensitive layer is
a direct function of the thickness desired in the
relief image and this will depend on the subject
being reproduced and the ultimate use of the relief,
e.g., thick soft reliefs are useful for flexograp'nic
20 printing and thin hard reliefs are useful for
planographic printing. In general, the thickness of
the polymerizable layer will be less than about 0.250
inch, e.g., it will vary from about 0.0005 to about
0.250 inch (0.00127-0.635 cm) and layers within this
25 range of thickness will be used for the majority of
the printing plates.
~ etween the photosensitive layer and
flexible support described above is preferably placed
a layer of an adhesive blend which comprises at least
30 two polymers taken from a group of the following four
polymers:
(1) Polyester resin, a condensation polymer
of ethylene glycol, terephthalic acid, isophthalic
acid and azelaic acid in a molar ratio of about
35 6:2:1:3 have a Mn of 19,000 and Mw of 37,000;
1~4891
17
(2) Polyether polyurethane resin, a
crystalline, thermoplastic resin having a Brookfield
viscosity of 100-1200 centipoises using 15% by weight
solids in methyl ethyl ketone and a Brookfield
5 spindle #3 at 12 rpm, and an adhesive activation
temperature in the range of 54 to 63C. The
polyether polyurethane has an elongation at yield of
15%, elongation at break of 615%, modulus at 400%
elongation of 600 psi (42.18 kg/cm2),
decrystallization temperature of about 49C;
(3) Polyamide resin, a translucent light
amber color, Ball and Ring softening point of
132-145C, melt viscosity of 40 to 60 poises at
210C, flash point greater than 299C, percent water
absorption for 1 day is 0.7, for 7 days is 1.6,
tensile yield of 460 psi (32.34 kg/cm2), tensile
break of 450 psi (31.64 kg/cm2) and elongation of
560%. (The tensile yield, tensile break and
elongation are determined at 24C according to ASTM
20 Procedure D-1708); and
(4) Polyamide resin, a translucent light
amber color, Ball and Ring softening point of
150-160C: viscosity of 28-38 poises at 210C,
percent water absorption for 1 day is 1.5, for 7 days
25 is 2.8, and
-18C 24C 60C
Tensile 980 (68.893 400 (28.12) 70 (4.92)
- yield,
psi
30 (kg/cm2)
Tensile 2200 (154.66) 360 (25.31) 50 (3.52)
break,
psi
( kg/cm2 )
elongation 350 250 40
(~)
1~:7489~ .
18
(The tensile yield, tensile break and elongation are
determined at the stated temperatures according to
ASTM Procedure D-1708).
The number average molecular weights (~n) of
the resins can be determined by gel per~eation
chromatography (GPC) employing a known standard,
e.g., butadiene, as known to those skilled in the
art. The weight average molecular weights (~Iw) of
the resins can be determined by using a light
scattering technique using known standard samples,
e.g., polystyrene, polymethacrylic acid,
polymethylmethacrylate, etc., as known to those
skilled in the art.
The particular polymers can be present in
the adhesive blend in the following ranges based on
the total weight of resin in the adhesive
composition: (1) 0 to 78% by weight, (2) 0 to 78% by
weight, (3) 0 to 94% by weight, and (4) 0 to 97% by
weight. Preferred adhesive blends containing four,
three and two resin components are set forth below
wherein the percentages are by weight based on the
total resin content.
Percentage ranges for the quaternary
adhesive blend are:
(1) 25 to 31%, preferably 25%,
(2) 25 to 31%, preferably 25%,
(3) 25 to 19%, preferably 25%, and
(4) 25 to 19%, preferably 25%.
Percentage ranges for two tertiary adhesive blends, A
30 and B, are:
A. (1) 1 to 78%, preferably 1 to ~5%,
(2) 1 to 78%, preferably 1 to 65%, and
(3) 1 to 94%, preferably 1 to 90%; and
B.(1) 1 to 63%, preferably 1 to 45%l
35(3) 1 to 93%, preferably 1 to 85%, and
(4) 1 to 97%, preferably 1 to 90%.
18
1~74E~91
19
Percentage ranges for five binary adhesive blends, C
to G, are:
C. (1) 7 to 77%, preferably 15 to 50%, most
preferably 30~ and
(3) 93 to 23%, preferably 85 to 50%, most
preferably 70%.
(This adhesive blend is particularly preferred.)
D. (l) 3 to 60~, more preferably 5 to 30%, and
(4) 97 to 40~, more preferably 95 to 70~,
E. (1) 23 to 77%, more preferably 35 to 45%, and
(2) 77 to 23%, more preferably 65 to 55~.
F. (2) 10 to 16%, preferably 25 to 30%, and
(4) 90 to 40~, preferably 75 to 70%; and
G. (2) 7 to 72~, preferably 15 to 50%, and
(3) 93 to 28%, preferably 8S to 50%.
The adhesive blends of this invention
provide an adhesion value for the photosensitive
layer to the support of at least 3 lbs/inch (53.57
kg/m) and generally much greater adhesion, e.g., in
~0 the range of 8 lbs/inch ~142.86 kg/m) or more. These
adhesion values are sufficient when the elements of
the invention are used as printing plates,
particularly flexographic printing plates.
The adhesive blends preferably contain
additives such as antiblocking agents, colorants,
e.g., dye, etc. Useful antiblocking agents include:
preferably polyolefin particles or beads but also
other hard particles or beads such as silicon
dioxide, etc. Dioctyl sodium sulfosuccinate, a
surfactant, can be used. A preferred polyolefin
material is described in the examples. The bead size
of the antiblocking agents can be greater than the
thickness of the adhesive layer resulting in beads
partially protruding out of the layer of the adhesive
35 blend. Such a configuration appears to have little
19
;
1~74~91
or no effect on the degree of adhesion. Many types
of colorants or dyes are also useful in the adhesive
layer. A preferred dye is Du Pont Milling Blue BL
(CI Acid Blue 59). Other useful dyes include:
Methylene Violet (CI Basic Violet 5), LUXOL* Fast
Blue MBSN (CI Solvent Blue 38), PONTACYL* Wool Blue
BL (CI Acid Blue 59 or CI 50315), PONTACYL Wool Blue
GL (CI Acid Blue 102 or CI 50320), Victoria Pure Blue
BO (CI Basic Blue 7 or CI 42595), C.I. 109 Red Dye,
Rhodamine 3 GO (CI Basic Red 4), Rhodamine 6 GDN
(CI Basic Red 1 or CI 45160), Fuchsine dye (CI 42510),
Calcocid Green S (CI 44090) and Anthraquinone Blue 2
GA (CI Acid Blue 58).
~n adhesive solution is prepared by adding
the ingredients generally in the following order
to the solvent with continuous stirring: polymers,
polyolefin antiblocking agent, colorants. Useful
solvents include mixtures, e.g., methylene
chloride/ethyl acetate, methylene chloride/n-butyl
acetate, methylene chloride/cyclohexanone, methylene
chloride/methanol/Cellosolve~, etc., and preferably
a mixture of methylene chloride/Cellosolve~, 90/10
parts. Additional solvent can be added to make up
any weight loss. The choice of solvents is governed
by the need to provide the fastest practical drying
rates without blistering the coating and without
leaving behind small amounts of solvent. The
solvents should also have a solubilizing effect on
the dyes that may be present.
The adhesive solution is then applied to
the flexible support by known means, e.g., coated by
use of a doctor blade or in a commercially available
continuous web coater-drier to provide a dry coating
weight in the range of about 80 to 500 mg/dm2 prefer-
35 ably about 260 to 300 mg/dm2. A most preferred
* denotes trade mark
1~74fl~
21
coating weight of the adhesive layer is about 260
mg/dm . Generally, the adhesive layer has a dry
thickness of 0.0008 to 0.001 inch (0.020 to 0.025
mm). In a continuous coating the web speed can vary,
e.g., 15 to 150 feet/minute (4.57 to 45.72 m/minute).
The drying temperature ranges from 60 to 130C,
preferably 80-90C.
A preferred flexible support is
flame-treated polyethylene terephthalate, 0.001 to
0.007 inch (0.025 to 0.18 mm) thick, preferably 0.005
inch (0.13 mm) in thickness. Flame-treatment of
polymeric films is known. The following U.S. patents
describe useful procedures and apparatus for flame
treating polymeric films: Bryan U.S. Patent 3,145,242,
and Thompson U.S. Patents 3,360,029 and 3,391,912.
The fuel equivalence ratio of the combustible gas
mixture, ~, is 1.4 which is equal to 5(propane flow
rate)/[(oxygen flow rate) + (0.21 air flow rate)].
All 1OW rates are in standard cubic feet or cubic
liters/minute. The web speed is 175 lineal
feet/minute (53.34 m/minute).
The dried adhesive coated support can be
adhered immediately to the photosensitive layer
or can be stored for subsequent adherence. The
adhesive-coated support can be laminated to the
photosensitive layer in a press, e.g., at 140 to
160C at a pressure of 20,000 to 30,000 psi ~1406
to 2109 kg/cm2) for up to about three minutes,
followed by cooling in the press to less than 60C.
Preferably the photosensitive element is prepared
by calendering. The photosensitive layer, which
preferably is formed by extruding through a die, has
present on the side remote from the side adjacent
the adhesive layer a 0.005 inch (0.13 mm) thick
~1748~1
~2
polyethylene terepht'nalate film which subsequently
acts as a protective cover sheet. Other films can be
used such as polystyrene, polyethylene, polypropylene
or other strippable material. There preferably is
present between the photosensitive layer and the rilm
cover sheet a thin hard, flexible, solvent-soluble
layer, such as a flexible, polymeric film or layer,
e.g., a polyamide or a copolymer of ethylene and
vinyl acetate. The flexible polymeric film remains
on the photosensitive layer after removal of the film
cover sheet described above. The flexible polymer
film protects for reuse an image-bearing negative or
transparency superposed thereon or improves contact
or alignment with the photosensitive surface. ~rior
15 to the imagewise exposure using the sources described
below, the element is exposed through the support to
polymerize a predetermined thickness of the
photosensitive layer adjacent the adhered support.
This polymerized portion of the photosensitive layer
20 is designated a floor. The floor thickness varies
with the time of exposure, exposure source, etc. The
exposure is generally for 1 to 30 minutes.
Printing reliefs can be made in accordance
with this invention by exposing to actinic radiation
25 selected portions of a photosensitive layer of an
element described above, for example, through a
process transparency, i.e., an image-bearing
transparency or stencil having areas substantially
transparent to actinic radiation and of substantially
30 uniform optical density and areas opaque to actinic
radiation and of substantially uniform optical
density until substantial addition-polymerization or
photocrosslin~ing takes place. During the
addition-polymerization or crosslinking, the
~1748~ ~
23
butadiene polymer/ethylenically unsaturated compound
composition is converted to the insoluble state in
the radiation-exposed portions of the layer, with no
significant polymerization or crosslinking taking
place in the unexposed portions or areas of the
layer. The unexposed portions of the layer are
removed by means of a li~uid developer for the high
molecular weight butadiene polymers. The process
transparency may be constructed of any suitable
material including cellulose acetate film and
oriented polyester film.
Actinic radiation from any source and of any
type can be used in the photopolymerization process.
The radiation may emanate from point sources or be in
the form of parallel rays or divergent beams. By
using a broad radiation source relatively close to
the image-bearing transparency, the radiation passing
through the clear areas of the transparency enters as
divergent beams and thus irradiates a continually
diverging area in the photosensitive layer underneath
the clear portions of the transparency. This results
in a polymeric relief having its greatest width at
the bottom of the photosensitive layer, i.e., a
frustum, the top surface of the relief being the
dimensions of the clear area.
Inasmuch as the free-radical generating
systems activatable by actinic radiation generally
exhibit their maximum sensitivity in the ultraviolet
range, the radiation source should furnish an
effective amount of this radiation, preferably having
a wavelength range between about 2500 A and 5000 A.
Suitable sources of such radiation, in addition to
sunlight, include carbon arcs, mercury-vapor arcs,
fluorescent lamps with ultraviolet radiation-emitting
3; phosphors, argon glow lamps, electron flash units and
23
- 1~7489~
24
photographic flood lamps. Electron accelerators and
electron beam sources through an appropriate mask may
also be used. Of these, the mercury-vapor lamps,
particularly the sun lamp or "black light" type, and
the fluorescent sun lamps, are most suitable.
The radiation exposure time may vary from
fractions of a second to minutes, depending upon the
intensity and spectral energy distribution of the
radiation, its distance from the composition and the
nature and amount of the composition available.
Customarily, a mercury vapor arc, a sunlamp or high
ultraviolet output fluorescent tubes are used at a
distance of about 1.5 to about 60 inches (3.8 to 152
cm) from the photosensitive composition. Exposure
temperatures are not particularly critical, but it is
preferred to operate at about ambient temperatures or
slightly higher, i.e., about 20 to about 35C.
After exposure, the image may be developed
by washing w~th a suitable developer. The developer
liquld ghould have good solvent or swelling action on
the butadiene polymer/ethylenically unsaturated
compound composition and little action on the
insolubilized image or upon the support or adhesive
layer in the period required to remove the
2S nonpolymerized or noncrosslinked portions. Suitable
developers include: organic solvents, e.g.,
2-butanone, benzene, toluene, xylene,
trichloroethane, trichloroethylene, methyl
chloroform, tetrachloroethylene, and solvent
mixtures, e.g., tetrachloroethylene/n-butanol, etc.
When the high molecular weight butadiene polymer
component contains carboxyl groups, suitable
developers include: aqueous base to which a
water-soluble organic solvent may be added~ Suitable
specific developer mixtures include sodium
,
117~
2~
hydroxide/isopropyl alcohol/water, sodium
carbonate/water, sodium carbonate/2-butoxyethanol/
water, sodium borate/2-butoxyethanol/water, sodium
silicate/2-butoxyethanol/glycerol/water, sodium
carbonate/2-(2-butoxyethoxy)ethanol/water and sodium
hydroxide (0.5 weight percent) in 16.6 volume percent
2-(2-butoxyethoxy) ethanol in water, which is
preferred. The particular developer combination
chosen will depend upon the carboxyl content of the
photosensitive composition and the properties and
amounts of the binders employed. Other aqueous
developer combinations which may be employed are
described in U.S. Patent 3,796,602. These aqueous
base/water-soluble organic solvent combinations may
be preferred in some cases because of their low
cost, nonflammability and reduced toxicity.
Development may be carried out at about
25C, but best results are sometimes obtained when
the solvent is warm; e.g., 30-60C. Development
time can range from 1 to 120 minutes, preferably
1 to 25 minutes.
In the development step where the relief
is formed, the developer may be applied in any
convenient manner, as by pouring, immersion,
spraying, or roller application. Brushing aids in
the removal of the unpolymerized or uncrosslinked
portions of the composition. When the printing
plate undergoes aqueous development, a water rinse
is subse~uentially applied, e.g., for about 5 to
300 seconds to the developed plate to remove traces
of developer from the plate surface. The term
"aqueous development" includes the water rinse.
1174f~
26
After solvent development, the printing
plate is dried at a temperature in the range of room
temperature to about 125C, preferably 60C for one
hour. After aqueous development the printing plate
may be dried, but it has been found that the rinsed
aqueous developed plate while still wet can be
contacted with the aqueous bromine-containing
solution. Hot air drying can be accomplished by use
of a forced hot air drier or other suitable dryer.
The plate is then contacted with an aqueous
solution having a free bromine concentration of 0.01
to 3.5~ by weight and pH of 0.7 to 6.5, for about
15 seconds to 20 minutes. The plate can either be
flooded with the aqueous bromine solution or can be
dipped in the bromine solution, the latter being
preferred. It is preferred to maintain the bromine
solution in contact with the printing plate for from
15 seconds to 10 minutes, more preferably from 30
seconds to 2 minutes. The bromine solution is
preferably used at ambient temperature but can be
heated up to about 35C. The bromine-containing
solution can be prepared by addition of bromine,
mixtures of alkali, e.g., sodium, potassium, etc.,
bromate-bromide-acid, e.g., hydrochloric acid,
sulfamic acid, hydrobromic acid, etc., in water.
Complexes containing bromine such as described in
German Patent A~plication 2,823,300, published
December 13, 1979 can be used to make the bromine-
containing solution. The bromine-containing solution
can also be prepared by mixing an alkali, e.g.,
sodium, potassium monopersulfate and a bromide salt,
e.g., sodium, potassium bromide, in aqueous solution
as disclosed in assignee's copending Canadian
Application Serial No. 402,367, filed May 06, 1982
26
~7~91
27
entitled "Process for Bromine Surface Treatment of
Photosensitive ~lastomeric Flexographic Printing
Plates".
The printing plate, after development, can
be postexposed to a source of actinic radiation,
either prior to or subsequent to the above-described
bromine treatment. The postexposure is generally for
5 to 15 minutes duration preferably to the actinic
radiation source used for the imagewise exposure.
After both treatments the printing plate is ready
for use.
BEST MODE FOR CARRYING OUT THE INVENTION
The best mode is illustrated in Example 1.
INDUSTRIAL APPLICABILITY
The printing reliefs prepared from the
photosensitive flexographic elements of the invention
can be used in all classes of printing but are most
applicable to those classes of printing wherein a
distinct difference of height between printing and
nonprinting areas is required and particularly to the
flexographic printing class wherein a resilient print
area is required, e.g., for printing on deformable
printing surfaces. These classes include those
wherein the ink is carried by the raised portion of
the relief such as in dry-offset printing, ordinary
letterpress printing, the latter requiring greater
height differences between printing and nonprinting
areas, and those wherein the ink is carried by the
recessed portions of the relief such as in intaglio
printing, e.g., line and inverted halftone. The
plates are particularly useful for multicolor
printing.
The relief and printed images obtained show
fidelity to the original transparency both in small
detail and in overall dimensions even when the
~74891
28
element is imagewise exposed on a cylindrical
support. The reliefs have high impact strength, are
tough and abrasion-resistant, have broad ink
compatibility, and have improved solvent resistance.
EXAMPLES
The following examples illustrate the
invention wherein the parts and percentages are by
weight.
Ink/Solvent CompatibilitY Test
The following procedure is used to determine
the compatibility and usefulness of printing inks and
solvent with flexographic printing plates having a
layer of the photosensitive, elastomeric composition
described herein. An exposed, developed printing
plate, after determination of its thickness, Shor~A
hardness (ANSI/ASTM D2240-75) and weight, is immersed
for 24 hours in a particular solvent or ink. Upon
removal from the solvent or ink, and patting dry, the
thickness, Shore~A hardness and weight are
determined. If the changes in thickness ~QT)
expressed in inches (millimeters), Shore~A hardness
(~H), and weight (~%W) meet the following standards,
the printing plate is deemed to be compatible or
excellent (E) with respect to the solvent and/or ink:
~T: < 0.003 inch (0.076 mm~
~H: > -5 Shore~A units
~%W: < 3.5%.
When the following standards are achieved or exceeded
the printing plate is deemed to be incompatible or
unsatisfactory (U) with respect to the solvent and/or
ink:
~T: >0.012 inch (0.305 mm)
~H: <-20 Shor~A units
~W: >7.0%
_.
28
~7489~
29
In the intermediate range between the above two
standards the treated printing plates are of variable
or intermediate (I) utility with respect to the
solvent and/or ink. The overall ratings are set
forth in the Examples below.
Tack Test
The exposed, developed printing plate of
this invention can be tested for tackiness as follows:
(1) The surface is wiped clean with
isopropanol,
(2) Tissue such as Scott~ brand 510 toilet
tissue is pressed by means of a 500 g weight against
the plate surface (1 inch by 2 inches; 2.54 cm by
5.08 cm) for 30 seconds,
(3) The tissue is removed noting the
results:
(A) No tack - free from sticking
(B) Slight tack - sticks but peels
from sur~ace
~C) Tacky - peels but leaves a few
fibers on the plate
(D) Very tacky - sticks and tissue
rips upon peeling.
Skilled artisans learn to identify nontacky
or (A) grade printing plate surfaces by touch, i.e.,
finger-tip touch methods. Both methods have been
used. All treated samples below are tack free.
29
~748~
Example 1
An adhesive solution is prepared from the
following ingredients:
Ingredient Amount (parts)
Polyamide resin (3~, Lot No. OF52371 63.1
Polyester resin(l), 2 27.0
Polyolefin3 9.8
Du Pont Milling Blue BL dye, C.I. 0.1
Acid Blue 59
10 1 The polyamide resin, Macromelt~ 6238, a product
of Henkel Adhesives Company, a division of Henkel
Corp., 4620 West 77th Street, Minneapolis MN is
a translucent liqht amber color, has a Ball and
Ring Softening Point of 132-145C; melt viscosity
of 40 to 60 poises at 210C: flash point greater
than 299C; percent water absorption, 1 day is
0.7, 7 days is 1.6; tensile yield of 460 psi
(32.34 kg/cm2); tensile break of 450 psi (31.64
kg/cm2) and elongation of 560~. (The tensile
yield, tensile break and elongation are deter-
mined at 24C according to ASTM Procedure D-1708).
2 The polyester resin iæ the reaction product of
ethyiene ~lycol, terephthalic acid, isophthalic
acid and azelaic acid (molar ratio 6:2:1:3)
having a Mn of 19,000 and Mw of 37,000.
3 The polyolefin, Vestofine~SF-616, a product of
Dura Commodities Corp., 111 Calvert Street,
Harrison, New York, is snow white in color, has
a molecular weight of about 1,600, a density at
20C of about 0.96, penetration hardness at 25C
of 0.5 to 1.0, a melting point of about 118-128C,
particle size: about 85~ 10 microns or below,
about 15~ 10-20 microns.
The above ingredients are added in order to a
90/10 parts mixture of methylene chloride/Cellosolve~
to give a solution of about 16% solids. The polyolefin
beads do not dissolve. The mixture is stirred contin-
uously during and after the addition of the inqredients
to effect solution. Any weight loss during mixing is
made up by addition of methylene chloride.
The adhesive solution is applied to the
flame-treated surface of a polyethylene terephthalate
film support, 0.005 inch (0.13 mm) in thickness using
~7~9~1
31
a continuous web coater-drier to provide a dry coating
weight of about 260 mg/dm2. The web speed is 45 feet/
minute (13.72 m/minute) and the drying temperature is
86C (187F).
The adhesive-coated polyethylene terephthalate
support is placed adhesive side up in a steel platen
dammed to a thickness of 0.080 inch (2.03 mm), the
thickness of the finished printing plate. The adhesive-
coated support and platen are placed on a press and an
extruded sheet, 0.090 inch (about 2.29 mm) thick, of a
photopolymerizable composition on a 0.005 inch (0.13
mm) thick polyethylene terephthalate cover sheet bear-
ing a layer of a polyamide resin having a dry thickness
of 0.00017 inch (0.004 mm) is placed thereon with the
cover sheet side up, and is covered with a steel plate.
The cover sheet bearing the polyamide layer
is prepared by coating the polyethylene terephthalate
film with the following solution using an extrusion die
coater:
Ingredient Amount (%)
Methylene chloride 81.0
Methanol 2.0
N-methyl pyrrolidone 10.0
25 Polyamide resinl 7.0
1 The polYamide resin, Macromelt~6900, a product
of Henkel Adhesives Com~any, a division of Henkel
Corporation, 4620 West 77th Street, Minneapolis,
MM is essentially colorless, has a Ball and Ring
Softening Point, of 266-302F melt index at 347F;
of 5-15 g/10 minutes flash point 570F; percent
water absorption, 1 day is 0.2, 7 days is 0.5;
tensile yield of 1,200 psi; tensile break of 3,500
psi; and elongation of 540~. (The tensile yield,
tensile break and elongation are determined at
24C according to ASTM Procedure D-1708).
The extruded sheet of the photopolymerizable
composition is prepared from the following ingredients
which are blended and the blend is extruded at 170C
through a die.
31
.,
1~74891
32
Inqredient Amount ~parts)
Acrylonitrile~27)/butadiene 81.59
(70)/acrylic acid(3), high
molecular weight, (average
Mooney Viscosity is 45.0,
Hycar~ 1472x26 B.F. Goodrich
Chemical Co.
Hexamethylene diacrylate 10.0
Polyethylenesebacate4 5.0
10 Dibutyltin-S,S'-bis-isooctyl- 2.0
mercapto-acetate
2-Phenyl-2,2-dimethoxyaceto- 1.25
phenone
2,6-Di-t-butyl-4-methylphenol 0.10
1,4,4-Trimethyl-2,3-diazabicyclo- 0.05
(3.2.2)-non-2-ene-2,3-dioxide
Du Pont Milling Blue B~ dye, C.I. O.Ol(dry)
Acid Blue 59 (10% dispersion in
ethylene glycol)
4. Paraplex~ G-30, a low molecular weight
polyester resin manufactured by Rohm and
Haas, Philadelphia, PA.
The temperature is raised and pressure is gradually
applied which spreads the photopolymerizable s'neet
throughout the dammed area of the platen. After the
sheet is evenly distributed the temperature is raised
to 160C and pressure in the range of 20,000 to
30,000 psi (1406 to 2109 kg/cm ) is applied and
held for three minutes. The assembly is cooled in
the press to less than 60C by flowing water through
the press platens. The laminated element formed is
removed from the press and is placed support side up
in the exposure unit noted below. The element is
given an overall exposure in air at atmospheric
pressure for 4 minutes through the support to
32
polymerize a predetermined thickness of the
photopolymerizable layer adjacent the adhered suport.
This polymerized portion of the element is designated a
a floor.
After removal of the cover sheet the element
is then placed polyamide resin layer side up in a
Cyrel33040 Exposure Unit (registered trademark of E. I.
du Pont de Nemours and Company~ fitted with Sylvania
~L-VH0 fluorescent lamps. An image-bearing transpar-
ency (negative~ is placed on the element surface, and
tne element is exposed for 15 minutes while under
vacuum. The duration of exposure is a function of the
photopol~mer sheet thickness, thickness of the polymer-
ized floor and the type of image-bearing transparency
used.
After exposure the transparency is removed,
and the exposed element is placed in a rotary drum-brush
type Cyrel~3040 Processor. The unpolymerized areas of
the element and the entire polyamide resin layer are
removed in the processor by washing for 15 minutes with
0.5 weight percent sodium hydroxide in 16.6 volume
percent 2-(2-butoxyethoxy~ethanol in water followed by
a two minute water rinse. A 0.035 inch (0.89 mm) relief
image is obtained. The developed element (printing
plate~ is placed in a forced hot air drier or other
suitable drier and is dried at 60C for 15 minutes.
The dry plate is postexposed in air for 10 minutes
using the same exposure source used or the imagewise
exposure described above. The plate has a Shore~A2
hardness in the range of 56 to 60.
The dry printing plate is immersed for 2
minutes in an aqueous solution of potassium bromate-
potassium bromide having a solution pH of 1.2. The
bromine solution is prepared as follows: to 1800
ml of tap water i8 added 20 ml of conc. hydro-
chloric acid with mixing. To this solution is
33
.;
1174891
34
added with mixing a mixture of 200 ml tap water, 10 g
potassium bromide and 2.8 g potassium bromate (90.56%
H2O/8.81% HC1/0.49~ KBr and 0.14%~BrO3). The
free bromine concentration is 0.4~.
The changes in plate thickness~ hardness and
weight percentage of the exposed, developed and dried
printing plate using 2-propanol (50 vol. %)/mixed
hexanes (50 vol. %) in the Ink/~olvent Compatibility
Test described above are as follows:
~T: 0.004 to 0.0015 inch (0.102 to
0.038 mm)
H: 1.0 to 3.5
~ %W: 1.2 to 3Ø
All these values are better than the maximum standard
values set forth above for compatibility, and the
plate is rated E. The bromine-treated plate is
placed on a printing press and two million
impressions are produced using a cosolvent ink
(alcohol-hydrocarbon). This represents an excellent
press run. A Buna rubber printing plate (o~ten used
because of its high solvent resistance compared to
natural rubber) typically will yield only one million
impressions.
A similar dry printing plate without the
bromine treatment typically having ~ T of 0.0088 inch
(0.22 mm); ~H of -9.0 and ~W of about 4.8% varies
continuously in properties by swelling. This plate
is rated I. It normally is not press tested.
Example 2
This example compares the ink/solvent
compatibility of bromine and chlorine treated
photosen~itive flexographic printing plates described
in Example I except that the unexposed image areas
are removed by developing with 75 vol. ~
perchloroethylene/25 vol. % n-butanol, and there is
34
91 , ,,
no water rinse after development. The developed
plate is dried at 60C for 60 minutes. In Table 1 a
variety of solvent mixtures and/or other common
printing ink components are compared with respect to
5 ~T, ~H, ~%W, and a printing plate rating is set forth
for each sample.
Table 1
Treatment
Sam- Solvent or BrO3 (a)
El~ Mixture (%) ~Tmm ~H ,~%W Ratinq
1 1(100) 0.0051-0.3 1.0 E
2 1(100) 0.010-0.5 0.9 E
3 1(100) (c)
4 1(95),2(5) 0.0076-1.8 1.5 E
1(90),2(10) 0.028-2.0 2.2 E
6 1(80),2(20) 0.15-12.5 9.3
7 1(60),2(40) 1.30-20.5 43.3 U
8 1(90),3(10) 0.010-1.0 1.2 E
9 1(65~,3(35) 0.028-2.3 2.3 E
1(50),3(50) 0.038-3.5 3.0 E
11 1(95),4(5) 0.023-1.8 1.8 E
12 1(90),4l10) 0.066-5.3 4.4 E
13 1(80),4(20) 0.041-16.5 14.4
14 1(95),5(5) 0.01 -1.0 0.9 E
1(90),5(10) 0.013-1.0 1.2 E
20 16 1(80)~5(20) 0.015-1.3 1.5 E
17 6(20% in water) 0.01--1,3 0.6 E
18 6(100) 1.70-22.0 26.8 U
19 7(50)/H20(50) 0.0025 -0.3 0.3 E
~l7~89i
36
Table 1 (continued)
Treatment
Sam- Solvent or Cloro~ (b~
ple Mixture (%) ~Tmm LH ~%w Ratinq
1 1(100) 0.14 -9.3 5.0
2 1(100) 0.18 -10.3 4.7
3 1(100) ~c)
4 1(95),2(5) 0.048-15.0 7.8 U
1(90),2~10) 0.75 -20.311.8 U
6 1(80),2(20) 1.60 -24.524.5 U
7 1(60),2(40) 0.041-26.557.7 U
8 1(90),3(10) 0~28 -13.0 5.4
9 1(65),3(35) 0.27 -12.0 6.6
1(50)~3(50) 0.60 -16.0 7.8 U
11 1(95),4(5) 0.54 -18.810.0 U
12 :~30),4(10) 1.40 -20.020.5 U
13 1(80),4(20) 2.30 -27.042.8 U
14 1(95),5(5) 0.25 -13.0 5.6
1(90),5(10) 0.25 -14.0 6.1
16 1(80),5(20) 0.39 -12.8 7/1 U
17 6(20% in water) 0.018 -1.0 0.8 E
18 6(100) 2.0 -24.036.6 U
19 7(50)/H20(50) 0.0025 0 0.3 E
(a) Same treatment as Example 1
(b) 90 parts water, 9 parts Clorox~, 1 part
2 conc. HCL
(c) no treatment; ~T: 0.0088 (0.22 mm); ~H:
-9.0; ~W: 4.6; Rating I.
1 2-propanol 5 ethanolamine
2 ethyl acetate 6 ethyl Cellosolve~
3 mixed hexanes 7 ethylene glycol
4 2-nitropropane
From the results set forth in Table 1, it is
apparent that the bromine treatment in general yields
improved printing plates. The few Intermediate and
Unsatisfactory ratings resulting after bromine
treatment are observed for solvent mixtures that are
outside the normal solvent concentration ranges known
by those skilled in the art to be useful.
ExamPle 3
This example compares the ink/solvent
compatibility of bromine and chlorine treated aqueous
developed photosensitive flexographic printing plates
36
117~891
37
described in Example 1. In Table 2 below a variety
of solvent mixtures and/or other common printing ink
components identified by the numbers set forth in
Example 2 are compared with respect to ~T, ~H, ~W,
and an overall rating is set forth for each sample.
Table 2
Treatment
Sam- Solvent or Bro3 (a)
E~ Mixture (%~ ~Tmm a H ~%W Ratinq
1 1(100) 0.0051-0.3 1.0 E
2 1(100) 0.0025-0.8 1.1 E
3 1(100) 0.0051-1.2 1.8 E
4 1(100)
1(90),2(10) 0.051-8.2 5.8
6 1(90),2(10)
7 1(80),2(20) 0.20-16.8 12.4
8 1(80),2(20) 0.14-11.0 9.4
9 1(80),2(20)
15 10 1(60),2(40) 2.3-23.5 46.7 U
11 7(50)/H20(50) 0.0051 -1.0 0.3 E
12 7(50)/H20(50) 0 -1.3 0.3 E
Table 2 (continued)
Treatment
Sam- Solvent or Cloro~ (b)
20 ~le Mixture (%) ~Tmm ~H ~%W Ratinq
1 1(100) 0.13-9.3 4.6
2 1(100) 0.19-11.0 5.5
3 1(100)
4 1(100) 0.18-11.5 5.5 I(c)
1(90),2(10) 0.90-21.8 12.7 U
6 1(90),2(10) 0.59-21.5 12.1 U(d)
7 1(80),2(20) 1.50-25.5 23.6 U
8 1(80),2(20) 1.50-26.0 24.4 U
9 1(80),2(20) 1.40-25.5 23.6 U(e)
1(60),2(40) 2.10-25.8 55.8 U
11 7(50)/H2O(5o) 0.0076 -0.5 0.4 E
12 7(50)/H2O(5o) 0.0076 -1.3 0.4 E
(a) Same treatment as Example 1
(b) Same treatment as Example 2
(c), (d) ~nd (e) in Table 2 above which relate
to samples 4, 6 and 9, respectively, mean
that that particular sample is not Cloro~
treated.
117g~891
38
From the results set forth in Table 2, it is
noted that chlorine treatment has substantially no
effect with regard to ink solvents. Improved results
are achieved by the bromine treatment. In Sample 10
unsatisfactor~ results are achieved with a solvent
mixture outside the known useful concentration range.
Example 4
Example 1 is repeated except that the binder
component in the photosensitive elastomeric
composition is a high molecular weight acrylonitrile
(30~/butadiene(70) polymer (average Mooney Viscosity
is 54), Hyca~ 1053, B. F. Goodrich Chemical Co. The
results are set forth in Table 3 wherein the solvent
numbers are as set forth in Example 2. It is noted
that the bromine-treated examples have improved
solvent compatibility over the chlorine-treated
examples,
Table 3
Treatment
Sam- Solvent or BrO3 (a)
20 ~le Mixture (~) ~mm a H a%W Ratinq
1 1(100) 0.010 0 1.9 E
2 1(90),2(10) 0.064-1.2 4.7 E
3 1(80),2(20) 0.13 -6.0 10.4
4 1(50),3(50) 0.18 -5.5 8.3
Table 3 (continued)
Treatment
Sam- Solvent or Cloro~ (b)
Ple Mixture (%) ~Tmm ~H a%W Ratinq
1 1(100) 0.094 -3.8 3.9 I-E
2 1(90),2~10) 0.15 -4.5 10.8
3 1(80),2(20) 0.48 -14.0 22.1 U
4 1(50),3(50) 0.28 -10.8 11.8 I-U
(a) Same treatment as Example 1
(b) Same treatment as Example 2
38
117~891
39
Example 5
This example compares the ink/solvent
compatibility (solvent resistance) of bromine and
chlorine treated photosensitive flexographic ~rinting
plates prepared as described in Example 1 (Plate A-
aqueous development), Example 2 (Plate B solvent
development) and prior art flexographic printing
plates, e.g., 0.112 in¢h (~2.85 mm) in thickness,
containing styrene-isoprene-styrene block copolymer
known as Cyrel~II flexographic printing plate (Plate
C). Cyrel~ is a registered trademark of
E. I. du Pont de Nemours and Company, Wilmington,
DE. The bromine treatment is that described in
Example 1 and the chlorination treatment is that
described in Example 2.
Plate C is placed in an exposure unit, as
described below, and is given an overall exposure in
air through the support for a predetermined length of
time (for example, a 0.112-inch (~2.85 mm) thick
photosensitive layer requiring the polymerization of
an 0.080 inch (2.03 mm) portion of the layer is
exposed for about 3 minutes depending on lamp
intensity) .
The cover sheet is stripped from the
element. The surface is covered with an
image-bearing transparency, and the photosensitive
layer is imagewise exposed for 5 minutes under vacuum
in a Cyrel~3040 Exposure Unit (registered trademark
of E. I. du Pont de Nemours and Company) fitted with
Sylvania BL-V~O fluorescent lamps.
After exposure the transparency is removed,
and the exposed element is placed in a rotary
drum-brush type Cyrel~3040 Processor. The
unpolymerized areas of the element are removed in the
processor by washing with a mixture of 75 volume
~L74891
percent tetrachloroethylene/25 volume percent
n-butanol. The developed element (printing plate) is
placed in a forced hot air drier or other suitable
drier and is dried at 60C until the plate attains
its original thickness.
In Table 4 several solvent mixtures or other
common printing ink components (see numbers in
Example 2) are compared with respect to ~T, ~ %W
and a printing plate rating is set forth as indicated.
~748~1
41
Table 4
Solvent
or Plate Untreated
Mixture (~) Plate ~Tmm ~ Ratinq
8(100) A 0.15 -7.9 4.7
8(100) B 0.15 -5.3 5.8
8(iO0) c(a) _ _ _ U
1(90) and A 0.80-19.1 18.1 U
`9 (10)
1(90) and B 0.80-20.0 18.3 U
9 (10 )
1(90) and C 0.21 -6.0 7.3
9 (10 )
1(90),2(10) A 0.80 -20.8 10.7 U
I(90),2(10) C(b) - - E
1(100) A 0.13 -7.5 4.0
1(100) B(C) _ _ _ _
1(100) C(b) - - _ E
1174891
42
Ta~le 4 (continued)
Solvent
or Cloro~ Treated
Mixture (%) Plate ~Tmm ~H ,~W Rating
8(100) A 0.0051 -0.9 0.9 E
8(100) B 0.0076 -0.3 0.6 E
8(100) c(a) _ _ _ U
1(90) and A 1.4 -19.116.9 U
9 (10)
1(90) and B 1.3 -20.916.0 U
9 (10 )
1(90) and C 0.22 -7.3 6.4
9 (10)
15 1(90),2(10) A 0.6820.2 11.3 U
1(90),2(10) C 0.071-3.0 3.3 E
1(100) A 0.13 -9.2 4.8
1(100) B 0.14 -9.3 5.0
20 1(100) C 0.025-0.8 0.9 E
1~7489~
43
Table 4 (continued)
Solvent
or Bromine Treated
Mixture (%) Plate ~ Tmm ~H ~ %w Rating
5 8(100) A 0.0025-0.5 0.4 E
8(100) B 0 -0.4 0.6 E
8(100)(a) c(a) _ _ _ U
1(90) and A 0.0051-3.3 2.2 E
9(10)
1(90) and B 0.0076-3.1 2.4 E
9 (10)
1(90) and C 0.21-6.0 6.6
9 (10)
1(90),2(10) A 0.048 8.0 5.8 I-E
1(90),2(10) C 0.028 -1.0 2.0 E
1(100) A 0.013-0.8 1.6 E
1(100) ~ 0.00510.3 1.0 E
1(100) C 0.025-1.2 0.5 E
8 is a lower boiling fraction naptha,
distillation range 117C to 140C; 9 is
toluene;
(a) curled and swollen, no values can be
obtained;
(b) this control was not tested since plate is
designed for use with alcohol-acetate inks;
no detackification necessary;
(c) not determined.
From the results set forth in Table 4, the
ink/solvent compatibility of Plate C (Control) is not
appreciably affected by the chlorine or bromine
treatment. Plates A and B, however, show appreciably
improved ink/solvent compatibility when bromine
treated according to the invention as compared to
chlorine treated plates, particularly in those inks
containing alcohol solvents.
43
1~7489
44
ExamPle 6
This example illustrates the
interchangeability in the postexposure and bromine
treatment.
Photopolymerizable elements prepared as
described in Example 1 are placed support side up
under a bank of black fluorescent tubes also as
described in Example 1 and are exposed for 150
seconds. The elements are then imagewise exposed as
described in Example 1 for 10 minutes followed by
either a 16 minute wash with perchloroethylene
(75%)/n-butanol (25%) solvent or a 15-minute wash
with 0.5 weight percent sodium hydroxide in 16 volume
percent 2-(2-butoxy-ethoxy)ethanol in water. Each
developed element is postexposed as described in
Example 1 either preceded by or followed by a
2-minute bromine treatment as described in
Example 1. Each treated element is soaked in the
indicated solvent and the ~%W o~ the dry element is
détermined. The results are indicated in Table 5
wherein "before" indicates bromine treatment before
postexposure. The solvent/mixture numbers are set
forth in Example 2.
Table 5
25 Solvent/ Solvent Washout Aqueous Washout
mixture ~%W Q%w ~W ~W
~ Before After Before After
1(100) 0.99 1.05 1.06 1.00
1~80),2(20)9.26 9.15 9.37 9.57
1(60),2(40)43.30 42.20 46.70 47.40
7(50)H20(50)0.27 0.28 0.29 0.29
From the results set forth in Table 5, there is no
significant difference between the results obtained
by the two sequences.
44
1~4891
Example 7
This example illustrates the effect of
varying the time of bromine treatment.
Photopolymerizable elements are prepared as
5 described in Example 1 with the following variations:
Back exposure is 150 seconds,
Imagewise exposure is 10 minutes overall
~without image-bearing transparency) with
cover sheet retained,
Aqueous development is 15 minutes,
Forced hot air drying is 30 minutes,
Bromine treatment in minutes is 0, 1, 2, 5,
8 and 10.
The changes in plate thickness, hardness and
weight percentage are determined for each element for
the indicated treatment time expressed in minutes
according to the Ink Solvent Compatibility Test, and
the results are set forth in Table 6. The
solvent/mixture numbers are the same as set forth in
Examples 2 and 5. The values for the changes in
plate thickness (GT) are expressed in millimeters.
: 30
1~74~1
46
Table 6
Solvent/
Mixture
(%)
lOtlOO)1(100) 8(100) 11(100)
~T
0 0.590.13 0.15 1.3
1 0.043-0.015 0.023 0.0076
2 - 0.0025
0 0.0076 0.028 0.0051
8 - 0.0076
0.0076 -0.0025 0.0051 0.0~8
~H
O -12.8 -7.5 -7.9 -22.8
1 -2.5 -0.8 -2.0 -2.6
2 - -0.6
-0.9 -0.8 -1.1 -2.6
8 - -0.3
-1.4 -0.5 -1.1 -2.4
~%W
0 7.0 4.0 1.47 18.1
1 1.6 0.5 1.2 2.5
2 - 1.1
1.1 0.4 0.9 1.7
8 - 1.0
0.7 0.3 0.4 1.0
Rating
O U I I U
1 E E E E
2 - E
E E E E
8 - E
E E E E
l-propanol
11 n-butanol (60%) /LACTOL* spirits (40%).
LACTOL spirits is a mixture of aromatic and
aliphatic hydrocarbons marketed by Amsco
30 Company.
From the results set forth in Table 6, there
is no significant change in plate rating beyond a
treatment of one minute. All bromine treated samples
are rated excellent whereas the untreated samples are
rated either unsatisfactory (U) or intermediate (I).
* denotes trade mark
46
.. ~
~1748gl
47
EXAMPLE 8
A photosensitive printing plate is prepared
as described in Example 1 except that after aqueous
alk.aline development the printing plate is immersed
immediately in the aqueous bromine solution as
indicated in Example 1. The printing plate is then
dried and is postexposed as described in Example 1.
The printing plate is rated E.
~5
47
